This application claims priority under 35 U.S.C. §119(a) on Japanese Patent Application No. 2005-333034 filed in Japan on Nov. 17, 2005, the entire contents of which are hereby incorporated by reference.
The present invention is applied to image forming apparatuses that carry out image formation electrophotographically such as copiers, printers, and facsimile machines, and particularly relates to image forming apparatuses that are effective in removing toner that has adhered to a toner layer regulating blade in an image forming apparatus in which a nonmagnetic one-component development apparatus is installed.
Generally, in a nonmagnetic one-component development method, regardless of whether the toner is magnetic or nonmagnetic, a thin layer of charged one-component toner is formed on a developer bearing member and by conveying the thin layer by rotating a development roller to a development position facing a photosensitive drum on which a latent image has been formed, the latent image on the photosensitive drum is made manifest (developed). Here, in order to achieve a good image, it is essential that the toner thin layer is stably formed on the development roller so as to have a uniform charge and uniform thickness.
Generally, the charging of the toner layer on the development roller and the formation of the thin layer are carried out using a toner layer regulating blade that presses against the development roller with a predetermined pressure. In the charging of the toner layer and formation of the thin layer, toner adhesion to the toner layer regulating blade is caused due to long use, such that a good toner layer cannot be formed and may lead to image deterioration. That is, the toner layer regulating blade is continually in contact with the development roller with a predetermined pressure and due to frictional heat and the pressure thereof or environmental causes such as the temperature inside the apparatus, toner becomes attached (adhered) to the blade surface at contact positions where the toner layer regulating blade contacts the development roller and the vicinity thereof.
At first the adhered substance merely extends as a thin film on the surface and is at a level that presents no particular problem to image formation, but this builds up due to prolonged use and eventually exerts an adverse effect on images.
That is, the chargeability of the toner is worsened by the toner layer regulating blade due to the adhered substance, and the adhered substance blocks the inflow opening for toner between the toner layer regulating blade and the development roller, or forms mechanical roughness on the surface contacting the development roller, which leads to overall or local reductions in the toner layer thickness and local slippage (layer thickness increases), such that a uniform toner layer cannot be formed. As a result, for example, the density in images is reduced, and partial white streaks or partial black streaks (in the case of monochrome) appear.
Accordingly, to address these problems, development apparatuses are proposed that perform cleaning on the toner adhesion substance on the toner layer regulating blade (for example, see JP S61-243473A (hereinafter, “patent document 1”) and JP H04-281478A (hereinafter, “patent document 2”)).
The development apparatus of patent document 1 is configured so that in a development apparatus that develops an electrostatic latent image opposing a photosensitive drum using a one-component developer, the development roller is rotated by a predetermined angle at a non-development time in a direction reverse to that during development. Here, “predetermined angle” is an angle between a first toner layer regulating blade and a second toner layer regulating blade, which from FIG. 1 thereof is an angle of approximately 150 degrees.
Furthermore, in the development apparatus of patent document 2, when a printer apparatus is powered up, the development roller is rotated continuously for one minute in a direction reverse to that during development, then stopped for development to begin.
Thus, apparatuses have already been proposed that remove toner adhered to the toner layer regulating blade by rotating the development roller in a direction reverse to that during development.
However, with the development apparatus of patent document 1, since the angle for reverse rotation is as much as 150 degrees, there is a problem of outflow of toner from the development tank due to reverse rotation of the development roller. For this reason, in patent document 1, a second toner layer regulating blade is provided on a downstream side of the development region in order to prevent outflow of toner from the gap between the development roller and the development tank. That is, the second toner layer regulating blade is provided only for the purpose of preventing outflow of toner due to reverse rotation of the development roller. Furthermore, there is no mention whatsoever in patent document 1 as to whether or not the photosensitive drum is also made to rotate in reverse at the time of reverse rotation of the development roller. Consequently, in the case of causing only the development roller to rotate in reverse while the photosensitive drum is stopped, there is a problem of unnecessary friction on the contact surface thereof.
Moreover, with the development apparatus of patent document 2, since the driving for the reverse rotation of the development roller continues for as long as one minute, there is a problem even more than with patent document 1 of outflow of toner from the development tank due to reverse rotation of the development roller. However, no countermeasure whatsoever is conducted in regard to this in the development apparatus of patent document 2. Furthermore, since the drive motor for the photosensitive drum is also turned on during reverse rotation of the development roller, reverse rotation is performed while the development roller and the photosensitive drum are in a state of contact, which presents a problem of unnecessary friction being caused at both contact surfaces.